To image the possible alterations in brain regional GABAA receptor subtype properties in a genetic animal model of human anxiety, mice heterozygous for the deletion of GABAA receptor γ2 subunit (γ2+/-) were studied using ligand autoradiographic assays on brain cryostat sections. The [35S]TBPS binding assay was designed to reveal impaired GABA and channel site coupling shown to be more prominent in recombinant α1/6β3 than in α1/2β3γ2 or β2 subunit-containing GABAA receptors expressed in HEK 293 cells. Increased GABA-insensitive [35S]TBPS binding in the γ2 +/- mouse brains was evident in the cerebral cortex and in subcortical regions, the alterations being regionally similar to the loss of γ2 subnunit-dependent benzodiazepine (BZ) sites as revealed by [ 3H]Ro 15-4513 autoradiography. As the γ2 subunit protein is needed for synaptic clustering of GABAA receptors, these results indicate that the extrasynaptic αβ3 receptors can be visualized in vitro as atypical GABA-insensitive [35S]TBPS binding sites. The results suggest that GABAAergic synaptic inhibition is widely decreased in the brains of anxiety-prone γ2+/- mice, while extrasynaptic GABAA receptors are increased. These autoradiographic imaging findings further demonstrate the need to develop GABAA receptor subtype-selective in vivo ligands to aid in assessing the contributions of various subcellular receptor populations in anxious and other patient groups.
All Science Journal Classification (ASJC) codes
- Cellular and Molecular Neuroscience
- Cell Biology